Deicer composition

ABSTRACT

A FLUID DEICER COMPOSITION PREFERABLY FOR USE TO DEICE AIRCRAFT RUNWAYS, CONSISTING OF FROM 22 TO 26 WEIGHT PERCENT OF UREA, 28 TO 34 WEIGHT PERCENT AMMONIUM NITRATE, AND 25 TO 30 WEIGHT PERCENT ETHYLENE GLYCOL IN WATER, TOGETHER WITH A SUFFICIENT AMOUNT OF A WATER SOLUBLE CHRO-   MATE SLATE TO PROVIDE FROM 0.05 TO 0.15 PERCENT CRO4=ION TO INHIBIT CORROSION OF ALUMINUM AND MAGNESIUM METALS.

Dec. 28, 1971 DISSOLUTION TEMPERATURE DISSOLUTION UTI H. F. SCOTT, JR., AL

DEICER COMPOSITION Filed May 15, 1969 TEMPERATURE VERSUS PERCENT H O OF DILUTION ICE AND 50 U ION 0;

2 T. /o A ONIU N 22.8 WT. UREA 22.5 wr. H 0 24.9 WT. ETHYLENE GLYCOL 0.2 WT. SODIUM CHROMATE 39.5 WT. /o AMMONIUM NITRATE 30.5 WT.% UREA 30.0WT.% WATER TOO H O OF DILUTION LVENT'UFPS F. SUU'T'T' JR.

u. NUVU'T'Ny United States Patent 7 3,630,913 DEICER COMPOSITION Herbert F. Scott, Jr., Prince George, and Joseph Novotny and Harry E. Ulmer, Hopewell, Va., assignors to Allied Chemical Corporation, New York, N.Y.

Filed May 15, 1969, Ser. No. 824,808 Int. Cl. C09k 3/18; C23f 11/18 U.S. Cl. 25270 6 Claims ABSTRACT OF THE DISCLOSURE A fluid deicer composition preferably for use to deice aircraft runways, consisting of from 22 to 26 weight percent of urea, 28 to 34 weight percent ammonium nitrate, and 25 to 30 weight percent ethylene glycol in water, together with a suflicient amount of a water soluble chromate salt to provide from 0.05 to 0.15 percent CrO ion to inhibit corrosion of aluminum and magnesium metals.

BACKGROUND OF THE INVENTION This invention relates to a chemical deicer composition and particularly pertains to a mixture of urea, ammonium nitrate, ethylene glycol and to a method of removing ice from aircraft runways by treatment with said composition.

A large number of the airports throughout the United States and other parts of the world experience snow and ice on the runways which must be cleared before normal operations may be resumed. The severity and frequency varies with respect to the geographic location. Although snow can be removed from runways adequately by existing equipment, there is no satisfactory mechanical manner of removing ice or counteracting its low traction. Ice on runways is considered to be particularly troublesome when it occurs in patches. The most promising method of combating the problem is to melt the ice with chemicals. The more common ice melting chemicals are calcium chloride and sodium chloride. These have been extensively employed to melt ice on roads, but they are too corrosive to be used on aircraft runways. The use of urea has been approved on the basis of no harm to aircraft by several major airlines. Other airlines have used urea with mixed results, primarily because of its limited effectiveness due to its relatively high eutectic point.

A deicer solution containing primarily formamide with other materials such as acetamide and urea is disclosed in U.S. Pat. 3,108,075. This fluid is stated to have negligible corrosion to aluminum and copper; however, no reference is made to corrosion of magnesium used in fabricating aircraft surfaces. Moreover, formamide is relatively expensive and has limited availability.

U.S. P'at. 3,185,648 relates to a solid deicer composition consisting of urea and ammonium nitrate and a corrosion inhibitor selected from the group consisting of trisodium phosphate and sodium polyphosphate. We have found that phosphates are good inhibitors for most metals but are not effective for magnesium which is used in fabricating aircraft surfaces. Chromates are also recommended.

While U.S. Patents 3,185,648 and 3,108,075 have contributed to the art, research in this field has continued in an effort to find still better deicing compositions that eliminate corrosion of both aluminum and magnesium metal surfaces of aircraft.

SUMMARY OF THE INVENTION An aqueous deicer composition consisting of from 22 to 26 percent by weight of urea, from 28 to 34 percent by weight of ammonium nitrate, from 25 to 30 percent by weight of ethylene glycol, based on the total weight of the Patented Dec. 28, 1971 composition, and containing a sufficient amount of a water soluble chromate salt to provide from 0.05 to 0.15 percent by weight of CrO ion, based on the total weight of the composition, to inhibit corrosion of aluminum and magnesium metals.

BRIEF DESCRIPTION OF THE DRAWING DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT This invention relates to a composition having a low freezing point which is particularly applicable to the deicing of aircraft runways.

The preferred deicer solution consists of 22 to 23 percent by weight urea, 29 to 30 percent by weight ammonium nitrate, 24 to 25 percent by weight ethylene glycol, and a soluble chromate salt in an amount to provide 0.1 percent by weight chromate ion, the remainder of the solution being water. A CrO level at least about 0.05 percent by weight is maintained although lower levels may be employed if less effective inhibition is acceptable. Levels as high as 0.15 percent and even higher are effective, although levels in excess of about 0.15 will usually not be used for economic reasons. Levels of about 0.1 percent are preferred. These low levels of CrO have been found to inhibit corrosion of both magnesium and aluminum, whereas other materials tested such as phosphate and polyphosphate salts were not effective inhibitors.

The preferred deicer composition of this invention can be stored at temperatures as low as about 10.4 F. without solidification of any of its components. Upon spraying the deicer solution on an iced runway, the eutectic temperature of the resulting mixture is about 16.6 F. As compared with solid deicers such as urea, the deicer solution of the present invention is particularly desirable due to ease of handling. By means of spray nozzles on a moving vehicle, the desired coverage of any area can be ac curately controlled. Solid deicers, on the other hand, are usually spread from the air, and, undesirably, drifts due to winds cause the deicer to miss the iced area on many occasions.

The composition of the present invention is a chloridefree fluid deicer composition which has a marked depressing action on the melting point of ice and which is essentially harmless to metal surfaces it may contact, including aluminum, magnesium, and their alloys. Moreover, the deicer composition of our invention is more effective as an ice melter on a weight basis than urea.

Our discovery is particularly useful in conjunction with melting ice and snow on airport runways, taxiways, bus and truck loading areas where most of the equipment is constructed of several metals, including aluminum and magnesium. However, if desired, utility of the invention may also be with the melting of ice and snow on roadways, sidewalks and the like.

The composition embodied herein may be prepared in any convenient manner providing a solution of the essential components. Urea and ammonium nitrate may be dissolved in water, either separately or combined, and then mixed in the proper proportions with ethylene glycol and chromate inhibitor. In any event, the method whereby the deicing composition embodied herein is prepared is not critical and is outside the scope of this invention. Any

method which produces solution of urea, ammonium nitrate, and ethylene glycol may be used.

The following examples are provided to more fully illustrate the instant invention. They are provided for illustrative purposes only and are not to be construed as limiting the invention, which is defined by the appended claims.

PREPARATION OF THE DEICER SOLUTION EXAMPLE I About 29.6 parts of ammonium nitrate and 22.8 parts of urea were added to 22.5 parts of water. The mixture was stirred and maintained at a temperature of 77 F. until all solids were dissolved. Then 24.9 parts of ethylene glycol were added to the solution, followed by 0.2 part of sodium chromate, tetrahydrate. and the mixture was stirred until sodium chromate dissolved. The resulting solution was stored at temperatures as low as l0.4 F. without salting out. The deicer was used effectively to melt ice at temperatures of from -11 F. to 32 F. However, the eutectic point was about -16.6 F.

EXAMPLE II The dissolution temperatures of various mixtures of the deicer solution of Example I and water were determined to obtain a phase diagram, as indicated by a solid line in the drawing. For comparative purposes, dissolution temperatures were also determined for mixtures of an aqueous ammonium nitrate-urea solution with water to obtain a phase diagram, as indicated by a dotted line which is superimposed in the drawing. It is apparent that the region of solution is larger for the deicer solution of the present invention. This factor is important in the deicing process since there is initially a limited supply of liquid water available on the surface of the ice and a large excess of deicer. As melting proceeds and water forms, the composition of the solution changes. Thus, at no time are the composition and physical characteristics of the mixture constant. A preferred deicer solution is one from which no solids separate at relatively low temperatures over a wide range of dilutions caused by the melted ice.

EXAMPLE III One problem encountered in developing this product was corrosion of bare magnesium. This was overcome by the chromate inhibitor as shown below:

Deicer solutions Weight percent 1 2 3 Ammonium nitrate ti o Urea .8 8 Ethylene glycl .5. 35.0 .5.0 Water '1 NtigCrO4.4II2O ......NHNHUH. l l

oi'rosion, Composition (Weight percent) zng.,sq. in

Deicer Solution 1no inhihiton. 173. 0 Deicvr Solution 20.1% inhibitor 14.6 Delcnr Solution 3+0.2% inhibitor 1. 4 Fifty percent deicer (0.2% inhibitor) plus 50% water 0. 7

Seven day immersion on bare magnesium.

EXAMPLE IV Thirty-six panels of six different aluminum alloys commonly used in aircraft construction were divided into three groups of six pairs of panels representing each alloy. Two groups of panels were used to test diluted and undiluted deice composition and the third group with water was used as control. Tap water, a 20 percent deicer solution, and a 100 percent deicer solution, prepared in Example I, were tested. The solution was applied to one side of each panel and two similar panels were placed together in sandwich style with the deicer solution between the two panels. The three groups of panels were exposed in a horizontal position at alternate intervals of sixteen hours in a humidity chamber and eight hours in an oven for a total of seven days. The humidity chamber was maintained at 100 F. and 98 to 100 percent relative humidity. The oven was maintained at 100 F. After exposure, the panels were rinsed in warm tap water and scrubbed lightly with a soft brush. After drying the panels were examined under X magnification and each panel was rated according to the following standard:

0-No visible corrosion l--Very slight corrosion or discoloration 2Slight corrosion 3Moderate corrosion 4-Extensive corrosion Results of the standard corrosion test are listed Rating deicer solution 100% deicer Tap water I solution Aluminum alloy control Number: 1

EXAMPLE V Hydrogen embrittlement test The deicer solution was tested by a standard hydrogen embrittlement procedure and found to be acceptable at 16-hour exposure of aircraft landing gear steel having a tensile strength of 200,000 p.s.i. or better.

EXAMPLE VI Deicing tests in field A solution applicator for applying the deicer consisted of a 1000-gallon stainless steel tank mounted on a tandem trailer. The rig was equipped with a 27-foot boom containing nine flood type nozzles on -inch centers to give a 30-foot swath. Solution was sprayed through the nozzles by a positive displacement type pump driven by a ground wheel drive.

(A) Field test with snow A taxiway covered with a sheet of ice one-sixteenth to one-eighth inch thick was treated with the deicer solution at rates of 15.5, 9.3, and 3.1 pounds per 100 square feet. An area treated at the highest rate had water standing on it 30 minutes after treatment. The air temperature during this test was 23 F. The next day all of the treated areas showed the effect of the deicer. The area treated with 15.5 pounds per 100 square feet Was 100 percent bare and the other areas were to percent bare. It is also noteworthy that the treated areas did not ice up during the next icing condition, indicating a residual effect of the deicer.

(C) Field test with packed snow Deicing tests were made on a concrete runway covered with 3 to 6 inches of hard packed snow. Two swaths were plowed the entire length of the runway, to remove most of the snow, leaving 75 to 80 percent snow-ice cover of one-fourth to one-half inch deep. Air temperature during the test was 15 to 18 F. One plowed area was treated at a rate of 6 pounds per 100 square feet; the other area at a rate of 3 pounds per 100' square feet. Within 20 minutes, deicer had dissolved the hard packed snow-ice to the point that large puddles of water were evident and ice remaining would break loose with little pressure. Water was evident along the entire section of treated runway. After one hour, the area treated with the 6 pounds per 100 square feet rate was 80 percent bare with the remaining 20 percent showing signs of melting. Four hours after treatment, both sections were 95 percent bare with patches of slush in the remaining percent.

We claim:

1. A fluid deicer composition comprising from about 22 to 26 weight percent of urea, from about 28 to 34 weight percent ammonium nitrate, from about 25 to 30 weight percent ethylene glycol in water, and a suflicient amount of water soluble chromate salt to provide CrO ion for inhibiting corrosion of metal selected from the group consisting of aluminum and magnesium.

2. A fluid deicer composition, according to claim 1, wherein the chromate salt is sufficient to provide from about 0.05 to 0.15 weight percent CrO ion to inhibit corrosion of aluminum and magnesium metals.

3. A fluid deicer composition, according to claim 1, wherein the chromate salt is sodium chromate tetrahydrate.

4. A method of causing deicing of snow, ice or mixture thereof, by applying a deicing composition thereto which comprises from about 22 to 26 weight percent of urea, from about 28 to 34 weight percent ammonium nitrate, from about 25 to 30 weight percent ethylene glycol in water, and a suflicient amount of water soluble chromate salt to provide CrO ion for inhibiting corrosion of metal selected from the group consisting of aluminum and magnesium.

5. A method according to claim 4 wherein the chromate salt is sufiicient to provide from about 0.05 to 0.15 weight percent CrO ion to inhibit corrosion of aluminum and magnesium metals.

6. A method according to claim 4 wherein the chromate salt is sodium chromate tetrahydrate.

References Cited UNITED STATES PATENTS 2,582,129 1/1952 Iacoby 25271 3,108,075 10/1963 Hearst 252 3,185,648 5/1965 Standish 25270 3,297,577 1/1967 Standish 252-70 LEON D. ROSDOL, Primary Examiner H. A. PITLICK, Assistant Examiner U.S. C1. X.R. 106-13; 252-689 

